The mission of the Southwest Oncology Group is to conduct clinical trials to prevent and treat cancer in adults, and to improve the quality of life for cancer survivors. The Group's network includes more than 5,000 physicians who practice at nearly 550 institutions, including 19 NCI-designated cancer centers. On average more than 7,000 cancer patients and healthy participants are enrolled each year in SWOG studies, and approximately 35,000 more are involved annually in ongoing clinical trials. During the last 25 years, more than 170,000 patients have participated in SWOG trials, while many more have received improved care as new standards of treatment or prevention are developed by the Group.